ath6kl: Protect ath6kl_cfg80211_vif_cleanup using rtnl_locks

ath6kl_cfg80211_vif_cleanup calls 'unregister_netdevice' which
inturn calls 'unregister_netdevice_queue' and it requires holding
rtnl_lock semaphore protection.
Signed-off-by: Mohammed Shafi Shajakhan <mohammed@qca.qualcomm.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>

drivers/net/wireless/ath/ath6kl/cfg80211.c

@@ -1535,7 +1535,9 @@ static int ath6kl_cfg80211_del_iface(struct wiphy *wiphy,
 
 	ath6kl_cfg80211_vif_stop(vif, test_bit(WMI_READY, &ar->flag));
 
+	rtnl_lock();
 	ath6kl_cfg80211_vif_cleanup(vif);
+	rtnl_unlock();
 
 	return 0;
 }